SOME CRYSTALLOCHEMICAL PECULIARITIES OF ALKALINE TOURMALINE BY INFRARED SPECTROSCOPY AND X-RAY ANALYSIS DATA
Keywords:
alkaline tourmaline, dravite, schorl, elbaite, isomorphism, IR-spectroscopy, X-ray diffractometry.Abstract
Collection of alkaline tourmaline samples from different deposits of the world, associated mainly with rare-metal pegmatites, has been investigated by means of infrared spectroscopy and X-ray diffractometry. The spectroscopic and structural features of the minerals of sсhorl–dravite series and elbayite are revealed. Dravite, schorl and elbaite IR-specrtra had shown the regular shift to the low-frequency side and splitting of some OH3 and OH1 IR stretching bands in course of isomorphic Mg2+ → Me2+ → Al3+, Mn2+, Li+ substitutions in Y-octahedra and Al3+ → Mg2+, Me2+→ Li+ – in Z-octahedra. The interpretation of spectral characteristics variability was confirmed by difference of elbaite and schorl–dravite series X-ray parameters, corresponding structural Y- and Z-octahedra sizes and their relationship that had shown the existence of two different fields for them on corre-sponding diagrams. Element cell parameter “a” is more sensitive to the tourmaline composition changes.The comprehensive tourmaline investigation allows to clarify its diagnostic and to estimate some structural features and isomorphous elements ratio.
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